This invention relates, in general, to softening cellulosic structures with cationic bond inhibiting compounds; and more specifically, to a composition having rheological properties which facilitate its use for enhancing the softness thereof. Most particularly, the invention relates to softening tissue paper webs and methods of producing such softened webs.
Sanitary paper tissue products are widely used. Such items are commercially offered in formats tailored for a variety of uses such as facial tissues, toilet tissues and absorbent towels.
All of these sanitary products share a common need, specifically to be soft to the touch. Softness is a complex tactile impression evoked by a product when it is stroked against the skin. The purpose of being soft is so that these products can be used to cleanse the skin without being irritating. Effectively cleansing the skin is a persistent personal hygiene problem for many people. Objectionable discharges of urine, menses, and fecal matter from the perineal area or otorhinolaryngogical mucus discharges do not always occur at a time convenient for one to perform a thorough cleansing, as with soap and copious amounts of water for example. As a substitute for thorough cleansing, a wide variety of tissue and toweling products are offered to aid in the task of removing from the skin and retaining such discharges for disposal in a sanitary fashion. Not surprisingly, the use of these products does not approach the level of cleanliness that can be achieved by the more thorough cleansing methods, and producers of tissue and toweling products are constantly striving to make their products compete more favorably with thorough cleansing methods.
Shortcomings in tissue products for example cause many to stop cleaning before the skin is completely cleansed. Such behavior is prompted by the harshness of the tissue, as continued rubbing with a harsh implement can abrade the sensitive skin and cause severe pain. The alternative, leaving the skin partially cleansed, is chosen even though this often causes malodors to emanate and can cause staining of undergarment, and over time can cause skin irritations as well.
Disorders of the anus, for example hemorrhoids, render the perianal area extremely sensitive and cause those who suffer such disorders to be particularly frustrated by the need to clean their anus without prompting irritation.
Another notable case which prompts frustration is the repeated nose blowing necessary when one has a cold. Repeated cycles of blowing and wiping can culminate in a sore nose even when the softest tissues available today are employed.
Accordingly, making soft tissue and toweling products which promote comfortable cleaning without performance impairing sacrifices has long been the goal of the engineers and scientists who are devoted to research into improving tissue paper. There have been numerous attempts to reduce the abrasive effect, i.e., improve the softness of tissue products.
One area that has been exploited in this regard has been to select and modify cellulose fiber morphologies and engineer paper structures to take optimum advantages of the various available morphologies. Applicable art in this area includes: Vinson et. al. in U.S. Pat. No. 5,228,954, issued Jul. 20, 1993, Vinson in U.S. Pat. No. 5,405,499, issued Apr. 11, 1995, Cochrane et al. in U.S. Pat. No. 4,874,465 issued Oct. 17, 1989, and Hermans, et. al. in U.S. Statutory Invention Registration H1672, published on Aug. 5, 1997, all of which disclose methods for selecting or upgrading fiber sources to tissue and toweling of superior properties. Applicable art is further illustrated by Carstens in U.S. Pat. No. 4,300,981, issued Nov. 17, 1981, which discusses how fibers can be incorporated to be compliant to paper structures so that they have maximum softness potential. While such techniques as illustrated by these prior art examples are recognized broadly, they can only offer some limited potential to make tissues truly effective comfortable cleaning implements.
Another area which has received a considerable amount of attention is the addition of chemical softening agents (also referred to herein as xe2x80x9cchemical softenersxe2x80x9d) to tissue and toweling products.
As used herein, the term xe2x80x9cchemical softening agentxe2x80x9d refers to any chemical ingredient which improves the tactile sensation perceived by the consumer who holds a particular paper product and rubs it across the skin. Although somewhat desirable for towel products, softness is a particularly important property for facial and toilet tissues. Such tactilely perceivable softness can be characterized by, but is not limited to, friction, flexibility, and smoothness, as well as subjective descriptors, such as a feeling like lubricious, velvet, silk or flannel. Suitable materials include those which impart a lubricious feel to tissue. This includes, for exemplary purposes only, basic waxes such as paraffin and beeswax and oils such as mineral oil and silicone oil as well as petrolatum and more complex lubricants and emollients such as quaternary ammonium compounds with long alkyl chains, functional silicones, fatty acids, fatty alcohols and fatty esters.
The field of work in the prior art pertaining to chemical softeners has taken two paths. The first path is characterized by the addition of softeners to the tissue paper web during its formation either by adding an attractive ingredient to the vats of pulp which will ultimately be formed into a tissue paper web, to the pulp slurry as it approaches a paper making machine, or to the wet web as it resides on a Fourdrinier cloth or dryer cloth on a paper making machine.
The second path is categorized by the addition of chemical softeners to tissue paper web after the web is dried. Applicable processes can be incorporated into the paper making operation as, for example, by spraying onto the dry web before it is wound into a roll of paper.
Exemplary art related to the former path categorized by adding chemical softeners to the tissue paper prior to its assembly into a web (xe2x80x9cwet endxe2x80x9d addition) includes U S. Pat. No. 5,264,082, issued to Phan and Trokhan on Nov. 23, 1993 and in U.S. Pat. No. 5,543,067, issued to Phan on Aug. 6, 1996, the disclosure of each being incorporated herein by reference. Such methods have found broad use in the industry. However, such prior art compositions are either solids or viscous liquids at room temperature. As a result, such prior art chemical softening composition must be heated before dilution to a use concentration for addition to the papermaking furnish. Such heating adds complexity to the papermaking process and poses an additional capital requirement for the necessary equipment.
Further exemplary art related to the addition of chemical softeners to the tissue paper web during its formation includes U.S. Pat. No. 5,059,282, issued to Ampulski, et. al. on Oct. 22, 1991 incorporated herein by reference. The Ampulski patent discloses a process for adding a polysiloxane compound to a wet tissue web (preferably at a fiber consistency between about 20% and about 35%). Such a method represents an advance in some respects over the addition of chemicals into the furnish for the papermaking machine. For example, such means target the application to one of the web surfaces as opposed to distributing the additive onto all of the fibers of the furnish. However, when such softening compositions are used there may be a loss of control of the sheet as it is creped from the Yankee dryer. A widely believed theory is that the additives interfere with the coating on the Yankee dryer so that the bond between the wet web and the dryer is weakened.
Considerable art has also been directed toward the application of chemical softeners to already-dried paper webs either at the so-called dry end of the papermaking machine or in a separate converting operation subsequent to the papermaking step. Exemplary art from this field includes U.S. Pat. No. 5,215,626, issued to Ampulski, et. al. on Jun. 1, 1993; U.S. Pat. No. 5,246,545, issued to Ampulski, et. al. on Sep. 21, 1993; U.S. Pat. No. 5,525,345, issued to Warner, et. al. on Jun. 11, 1996, and U.S. patent application Ser. No. 09/053,319 filed in the name of Vinson, et al. on Apr. 1, 1998 all incorporated herein by reference. The ""626 Patent discloses a method for preparing soft tissue paper by applying a polysiloxane to a dry web. The ""545 Patent discloses a similar method utilizing a heated transfer surface. The ""345 Patent discloses methods of application including roll coating and extrusion for applying particular compositions to the surface of a dry tissue web. Finally, the Vinson, et al. application discloses compositions that are particularly suitable for surface application onto a tissue web.
While each of these references represent advances over the prior art, there is a continuing need for soft tissue paper products having good strength properties. There is also a need for improved softening compositions that can be applied to such tissue products to provide the requisite softness without adding additional complexity and capital expense to the manufacture of such products.
Such improved products, compositions, and methods are provided by the present invention as is shown in the following disclosure.
The present invention describes softening compositions that, when added to the wet end of a wet laid process for producing cellulosic structures, reduce the fiber to fiber bonding thereof, providing a structure with improved softness while providing acceptable strength and absorbency. The softening composition comprises:
an effective amount of a softening active ingredient;
a vehicle in which the softening active ingredient is dispersed;
an electrolyte dissolved in the vehicle, the electrolyte causing the viscosity of the composition to be less than the viscosity of a dispersion of the softening composition in the vehicle alone; and
a bilayer disrupter to further reduce the viscosity of the softening composition.
The term xe2x80x9ccellulosic structurexe2x80x9d as used herein is defined as a wet laid fabric, web, or sheet comprised of fibers containing cellulose. In its broadest sense, such structures possess a basis weight ranging from 10 g/m2 to about 1 kg/m2 and possess densities ranging from about 0.1 g/cc to as high as about 1 g/cc. The cellulosic structures of the present invention preferably derive at least a portion of their strength from the natural fiber to fiber bonds which form when a web of short cellulosic fibers is drained and dried from a aqueous slurry. Consequently, so called wet laid papermaking is the most common process employing the present invention.
The softening compositions of the present invention have desirable low viscosity at room temperature allowing dilution as a part of the papermaking process without the complexity and added cost of a heating step.
The term xe2x80x9cvehiclexe2x80x9d as used herein means a fluid that completely dissolves a chemical papermaking additive, or a fluid that is used to emulsify a chemical papermaking additive, or a fluid that is used to suspend a chemical papermaking additive. The vehicle may also serve as a carrier that contains a chemical additive or aids in the delivery of a chemical papermaking additive. All references are meant to be interchangeable and not limiting. The dispersion is the fluid containing the chemical papermaking additive. The term xe2x80x9cdispersionxe2x80x9d as used herein includes true solutions, suspensions, and emulsions. For purposes for this invention, all terms are interchangeable and not limiting.
The amount of the softening composition added to the cellulosic structure is preferably about 0.01% to about 10%, more preferably between about 0.03% and about 1% based on the total weight of the softening composition compared to the total weight of the resulting cellulosic structure.
The cellulosic structure is preferably a tissue paper, most preferably a tissue paper having a basis weight of from about 10 to about 100 g/m2 and a fiber density of less than about 0.6 g/cc.
All percentages, ratios and proportions herein are by weight, unless otherwise specified.